Methods of preparing 11-(3-dimethylaminopropylidene)-6-methyl-5,6-dihydromorphanthridines are disclosed in Belgian Pat. No. 732,405; Belgian Pat. No. 652,938; and British Pat. No. 1,207,116. The prior art methods possess the disadvantage of producing mixtures of the cis and trans isomer forms which often are undesirable because the pharmacological activity may reside in only one of the isomers.